Process for spinning polyamide filaments containing nucleating agents

ABSTRACT

A POLYAMIDE CONTAINING A POLYAMIDE NUCLEATING AGENT IS MELT SPUN.

P. R. THOMAS PROCESS FOR SPINNING POLYAMIDE FILAMENTS June 15, 1971 CONTAINING NUCLEATING AGENTS Original Filed Sept. 14, 1966 2 Sheets-Sheet 1 FIG. I! l MFIICFS. 2

m R M my PM m M M 0,3 6 m 6 m 6 0 w June 1971 P. R. THOMAS PROCESS FOR SPINNING POLYAMIDE FILAMENTS CONTAINING NUCLEATING AGENTS Original Filed Sept. 14, 1966 2 Sheets-Sheet 2 5-0 5/0' o-oasl- 0-1151 I 06! .3-

0-0/ 0/ 02 PMCtA TA 65 0F ADO/I'M.

ATTORNEEC/ 3,585,264 PROCESS FOR SPINNING POLYAMIDE FILA- MENTS CONTAINING NUCLEATING AGENTS Peter R. Thomas, Pontypool, England, assignor to Imperial Chemical Industries Limited, London, England Original application Sept. 14, I966, Ser. No. 579,273. Divided and this application Sept. 27, 1968, Ser. No. 834,915 Claims priority, application Great Britain, Sept. 14, 1965, 39,122/65 Int. Cl. B28b 3/20 US. Cl. 264-2I1 21 Claims ABSTRACT OF THE DISCLOSURE A polyamide containing a polyamide nucleating agent is melt spun.

This invention relates to filaments derived from polyamides i.e. condensation polymers wherein amide groups form an integral part of the polymer chain, and to a process for their manufacture.

This application is a division of our copending application Ser. No. 579,273, filed Sept. 14, 1966.

Polyamide filaments are most rapidly and economically obtained on a large scale by the extrusion of a molten mass of the polyamide, and, melt-spinning, as it is commonly referred to, has attained pre-eminence as the commercial method of manufacturing polyamide filaments.

In one typical melt-spinning method, the polyamide prepared by a conventional polymerisation process is cooled, broken into chips and dried. The chips are then melted and the molten fibre-forming material continuously pumped, by means of a metering pump, through a filter pack generally containing a fine-grained particulate material, and then extruded through the orifices in a spinneret under the pressure exerted on it at the back of the spinneret by the action of the pump. The freshly extruded filaments, which on emergence from the spinneret orifices are in the form of a viscous molten liquid, cool and elongate as they move away from the spinneret, the cooling often being assisted by a transverse or co'current stream of air flowing in a quenching chamber, often referred to as the chimney. The cooled and solidified filaments may then, as in polyhexamethylene adipamide (6.6 nylon) spinning, pass through a steam conditioner tube prior to passing over finish application rolls. Finally the filaments are wound up on a suitable support. In order that the filaments should achieve their maximum strength it is necessary that they be stretched by several, usually at least three, times their original length. This stretching normally referred to as drawing is carried out by passing the filaments between two sets of rotating rolls, the secnd set of rolls, drawrolls, rotating at a higher peripheral speed than the first, set, feed rolls, to impart the desired degree of stretch to the filaments which are then wound up on a bobbin or like support. A snubbing pin may be positioned between the two sets of rolls to locate the point of draw.

The point below the spinneret face at which the molten filaments solidify, hereinafter for convenience referred to as the solidification point, represents the point at which the mobility of the polyamide molecules has decreased, with the falling temperature, to such an extent that the viscosity of the material is sufficiently high to preclude, at

nitecl States Patent 0 least temporarily, for changes may subsequently occur as a concomitant to crystallisation, any further elongation of the filaments, thereby substantially stabilising the denier thereof. The temperature associated with the solidification point is below the normal melting point of the bulk solid polymer, and the spun filamentary material is therefore supercooled. Generally a high degree of supercooling of the spun filamentary material at the solidification point is considered to be desirable in, for example, minimising the growth of large spherulites which are Wellknown to have adverse effects on filament processability. In order to obtain the required high degree of supercooling it is necessary to impose a limit on the maximum spinning speed achievable in a particular spinning process, the actual value of this limit being dependant upon factors such as spun filament denier.

The elongation which the freshly extruded filaments undergo before solidification is generally referred to as the draw down. As well as reducing the denier of the filaments draw down also causes the molecules in the filaments to become oriented to some degree and there is some increase in the degree of orientation even after solidification. This orientation causes well-known birefringence effects to become visible when the filament is viewed transversely through a polarising microscope. Birefringence in the as-spun filaments, that is filaments which have not been subjected to an additional drawing process, is called the spun birefringence and its value may be determined by known techniques using a polarising microscope and a Berek compensator.

That a filament exhibits a measurable birefringence indicates that the segments of the polymer molecules which possess an intrinsic optical amisotropy must have a preferred orientation relative to the filament axis. Other techniques have to be employed to obtain more precise information on the nature of the preferred orientation. As is well-known one such technique is by means of the wide-angle X-ray Laue pattern from the fibre.

The Laue pattern exhibited by the fibre comprises two major rings, an inner and an outer ring, which are reflections from the principal paratropic lattice planes of the crystalline structure. The intensities of these rings (M) at meridian, the meridian being a straight line on the X-ray film parallel to the fibre direction and passing through the position of the primary X-ray beam, and (E) at equator, the equator being a straight line on the X-ray film perpendicular to the fibre direction and passing through the position of the primary X-ray beam, can be determined and orientation factors calculated. For convenience these orientation factors are designated 0, for the inner ring and 0 for the outer ring, by which terms these factors will be preferred to hereinafter.

In normal spinning of 6.6 nylon, for example, the orientation factors 0, and 0 as defined above for the asspun yarn are usually negative and often differ slightly in numerical value. The negative sign indicates that the c axis of the crystal lattice until cell, i.e. the molecular chain axis, is becoming oriented towards the filament axis, i.e. the structure may be described as having a preferred c axis orientation. The degree of orientation is generally low as indicated by the magnitude of the spun birefringence. In a fully drawn yarn of course the c axis orientation is high and 0, and tend to the value of 1.

If the orientation process is simply a progressive alignment of the molecular chains more and more parallel to the filament axis then 0 -0 for all degrees of orientation. However this condition frequently does not exist and it is considered that when (0 -0 differs from zero then the orientation process is more complex and it is useful to consider the size and magnitude of (0,0. In normal as-spun yarn of 6.6 nylon, for example, 0 is often numerically slightly larger than 0 and then (0 0,,) is small but positive, that it has a value in the range 0 to 0.2.

Generally the magnitude and nature of the spun orientation will control the degree of extrusion available in the drawing process to achieve the desired drawn yarn extension at break. It is well-known that the draw ratio subsequently required to be applied to an as-spun yarn to produce a drawn yarn having the desired extension at break,

decreases as the spinning speed is increased.

Surprisingly we have now found that polyamide filaments can be obtained by melt spinning which, in the asspun state, have values for (O -0 greater than 0.2 and that these filaments can be spun at higher speeds, i.e. wind up speeds, with consequent increase in productivity, than the previously known filaments having lower values for (0 -0 Such filaments exhibit a lesser degree of supercooling at the solidification point in the spinning process under otherwise comparable conditions, which has obvious process advantages.

Furthermore we have found that as-spun polyamide filaments in which (0,0 is greater than 0.2, and which have been spun at spinning speeds greater than about 1,500 ft. per minute, may be drawn at higher draw ratios than as-spun filaments in which (O -0 is less than 0.2 and which are spun at the same speed. Thus these filaments exhibit orientation characteristics which allow a further increase in spinning productivity to be obtained.

When the magnitude of (0 0,,) is large, i.e. greater than 0.7, 0 has a positive value and 0 a negative value.

This condition implies that the a axis of the crystal lattice unit cell is becoming oriented towards the filament axis, i.e. the structure may be described as having a preferred a axis orientation which contrasts with the preferred c axis orientation of the previously known asspun polyamide filaments.

Accordingly therefore, from one aspect, the present invention provides a yarn comprising one or more undrawn polyamide filaments having molecular orientations exhibiting X-ray reflection patterns in which (0 -0 is greater than 0.2. Preferably (0 -0 is greater than 0.7 and even more preferably 0, is greater than zero.

A feature of the present invention is that the change in spun orientation of the filaments enables a draw ratio for a required extension at break in the drawn yarn to be achieved which is largely insensitive to spinning speed.

The values of 0, and 0 are determined in the following manner.

The yarn sample is Wound as a parallel bundle of fibres on a fibre sample holder, which is then mounted in an evacuatable X-ray camera using a flat plate film. The camera is evacuated for a minimum period of 5 minutes (to a vacuum better than 0.2 mm. of Hg), and an exposure of 15 minutes at 40 kv. and 15 ma. is given to each sample, the cameras being continuously evacuated during the exposure. Ni filtered Cu. Ka radiation is used from a sealed X-ray tube operating in a Philips PW1008/30 generator.

The exposed film is processed as follows: 5 minutes in Ilford PQX-l X-ray film developer (at C.), 1 min. wash, 4 mins. in M & B Perfix fiscer (at 20 C.), followed by a min. or more Wash, to give a maximum optical density on the film of approximately 1.0.

Using a Joyce-Loebl double beam recording microdensitometer (Model E. 12 Mk III), diametrical scans are made across the equator and meridian of the diffraction pattern, the fibre axis being along the meridian. The two records are produced superimposed on one chart. A common background is drawn in before measurements are made of the intensity (E and M respectively) at the equaor and meridian for the two main reflections. The ratios M E d are then determined.

FIG. 1 of the drawings is a representation of an X-ray pattern obtained from an as-spun filament of 6.6 nylon of the present invention, indicating the reflections from the principal paratropic lattice planes of the crystalline structure which are used in the determination of the values of 0 and 0 FIG. 2 of the drawings is a representation of an X-ray pattern obtained from a normal as-spun yarn of 6.6 nylon. Comparison of the figures shows the nature of the orientation differences of the two filaments.

As examples of polyamides with regard to which the present invention is especially useful there may be mentioned polyhexamethylene adipamide (6.6 nylon) and polyhexamethylene suberamide (6.8 nylon).

The desired orientation may be induced in the as-spun polyamide filaments by the incorporation of at least 0.05, preferably 0.5 to 1.5, percent by weight of a finely divided nucleating agent in the polymer prior to spinning. The nucleating agent is preferably polymeric and should have an optical melting point greater than the melt holding temperature at spinning. Preferably the optical melting point of the polymeric nucleating agent is at least 10 C., or even more preferably at least 30 C., above the melt holding temperature at spinning.

The optical melting point of the polymeric nucleating agent is determined by observing under a microscope a sample of the material supported between glass slides that rest on an electrically heated stage; the melting point is taken as the temperature at which the optical birefringence of the sample disappears.

The melt holding temperature at spinning is defined as the temperature at the base of the melt pool above the booster pump in a conventional melt spinning unit such as is used in the manufacture of 6.6 nylon.

It is known to incorporate nucleating agent in polymers such as polyamides which are to be used in moulding and for making films, for example, to improve, inter alia, the transparency of the resultant product. However it has not been known to deliberately incorporate nucleating agents in polymers which are to be melt spun into textile filaments. According to another aspect, therefore, the present invention provides a process for the manufacture of a yarn consisting of undrawn polyamide filaments comprisrng incorporating a finely divided nucleating agent in a polyamide, forcing the molten polyamide containing the nucleating agent through a filtering medium, extruding the said polyamide through orifices contained in a spinneret plate and winding up the filaments.

Preferably the polymer contains at least 0.05% by weight, and more preferably 0.5% to 1.5% by weight of the nucleating agent.

Although it is preferred that the polymer should contain at least 0.05% of the nucleating agent, the actual lower limit for the concentration of the nucleating agent will depend upon the fineness of its state of division and may well be less than 0.01% by weight.

The term nucleating agent is to be understood to refer to solid substances which, when present in a finely divided state i.e. having a particle size less than 0.4a diameter in the as-spun polyamide filaments, induce the formation and growth of a crystalline texture which does not exhibit in the polarising microscope at the extinction positlon any discrete resolvable patterns characteristic of the well-known spherulites, i.e. the socalled Maltese cross pattern. Spherulite growth, if present, must therefore be limited to sizes approximately equal to or below the wavelength of visible light that is below about 1.5,u in diameter.

Polyamides having optical melting points greater than and preferably at least C. above the melt holding temperature at spinning of the base polymer may usefully be employed as nucleating agents. Especially effective are polyamides or copolyamides containing an aryl group in the polymer chain. As examples of this class of nucleants there may be mentioned polyamides comprising poly- (methylene) terephthalamide where x is an integer between 2 and 12 such as poly hexamethylene terephthalamide (6.T nylon), poly octamethylene terephthalamide (8.T nylon), poly decamethylene terephthalamide (10.T nylon) and poly dodecamethylene terephthalamide (12.T nylon). Copolyamides of the terephthalamides with other polyamides, e.g. poly hexamethylene adipamide/poly hexamethylene terephthalamide (6.6:6T) copolymer, polyhexamethylene adipamide/ poly octamethylene terephthalarnide (6.6:8T) copolymer, poly hexamethylene adipamide/ poly decamethylene terephthalamide (6.6: 10.T) copolymer, poly epsilon caprolactam/poly hexamethylene terephthalamide (6:6.T) copolymer and poly hexamethylene suberamide/poly hexamethylene terephthalamide (6.8:6.T) copolymer are particularly useful, the 6.6:6.T copolymer being the preferred nucleating agent for 6.6 nylon. The proportions of the aliphatic to aryl containing polyamides in the copolyamides to give the most effective nucleating agent for any given polyamide have to be determined by experiment, for the effective nucleation of 6.6 nylon by 6.6:6.T copolymer it is though that the copolymer should contain at least by weight, and preferably at least by weight of polyhexamethylene terephthalamide. Also effective as nucleating agents are poly p-Xylene adipamide and its copolymers with 6.6 nylon, and oly hexamethylene hexahydroterephthalamide and its copolymers with 6.6 nylon.

In addition to a nucleating agent the filaments of the present invention may also contain the usual range of additives such as delustering agents, pigments, antioxidants, stabilisers against the effects of heat and light, and so on and up to about 5% by Weight of another polyamide.

It has been observed that the filaments of this invention have a higher temperature at the solidification point in the spinning chimney i.e. show a lesser degree of supercooling, than previously known filaments. This effect can be readily verified while the filaments are being produced by chopping samples from the filament in either molten or solid form using known methods. After determination of the solidification point by this method the temperature associated with this point can be measured utilising a thermocouple or infra red pyrometer.

This increase in the temperature at the solidification point of the filaments in the chimney can be assessed more conveniently by the use of differential thermal analysis (D.T.A.) since, at a defined rate of cooling, the freezing point of a nucleated polymer is higher than the freezing point of the base polymer. This increase is usually of the order of at least 5 C. and may be as much as 10 C. D.T.A. freezing point can therefore be used to give an indication of whether or not a polyamide has been nucleated in a manner which will, when the polymer is melt spun, yield an undrawn yarn having the defined parameters. For example polyhexamethylene adipamide has a D.T.A. freezing point of about 223 C.; the inclusion of 1% of a (:50) 6.6:6.T copolymer may raise the said freezing point to 234 C.

D.T.A. freezing point is determined using a differential scanning calorimeter DSC-l available from the Perkin- Elmer Corporation, Norwalk, Conn., U.S.A. in combination with a recorder, the instrument sold as Model W by Leeds and Northup Co. being perfectly satisfactory. Differential power (i.e. the difference between the power supplied to test and control samples to maintain them at the same temperature and with the same rate of increase or decrease of temperature) which is equivalent to temperature, since the temperature increase or decrease is linear with time, is automatically plotted against time on the recorder. The temperature scale is automatically marked out on the side of the chart paper. In most instances it is convenient to determine on the same sample both its melting point, at a 20 C. per minute linear rate increase of temperature, and the solidification point, i.e. the freezing point of the molten material, using a 64 C. per minute rate of fall in temperature, although for the purposes of this specification, the latter point, which can be determined more accurately than the former, is generally the more significant.

The detailed method employed in conducting the D.T.A. test using the above rates of heating and cooling is as follows:

A sample of 5-15 mg. in weight is cut from polymer chip with a razor blade and sealed in an aluminum sample pan (as supplied by Perkin-Elmer) and placed in the DSC-l pan holder.

With dry nitrogen at room temperature flowing through apparatus at 25 cc./ min. the sample temperature is raised using manual control fairly rapidly (taking about 10 sees. for 200 C.) to 232 C. It is left at this temperature for 2 mins. for the whole sample to reach equilibrium, then the scanning speed of the instrument is set at 2 C./min., and the temperature of the sample automatically raised. The machine is left to run until the melt transition temperature has been passed when the curve which is being traced out by the recorder pen straightens out.

The temperature is then raised manually to the holding temperature, which, for any particular polymer, is the melt pool temperature of a spinning unit, e.g. 285 C. in the case of 6.6 nylon. The sample is held at this temperature for 2 mins. Then the scanning speed is set to 64 C/min., and the temperature automatically lowered at the required rate. When the transition is finished the temperature is lowered manually down to room temperature.

To take readings from the recorder chart so obtained, a ruler is placed along the portion of the trace immediately prior to the transition to establish the best straight base-line that the slightly uneven curve will fit onto, and the transition (solidification and/or melting) temperature is taken to be that point at which the curve first moves away from the base-line. This can be determined to bet ter than 1 C. accuracy.

The test is also used to determine the freezing point of undrawn i.e. as-spun filaments.

Various methods, some of which Will now be described in more detail, may be employed for introducing the nucleating agent into the polyamide.

For instance, in one method, herein for convenience referred to as the solution blending method, solutions of the polymer and nucleating agent in miscible solvents, are mixed together and the solute co-precipitated therefrom by the addition of a liquid in which it is insoluble. In employing this method it is often necessary, generally for the purpose of adjusting the proportion of nucleating agent in the polyamide to the desired level, to subject the co-precipitate, which may be regarded as a master batch of the nucleating agent in the polymer, in a suitable form to a further blending with additional polyamide. This further blending may be achieved by chip blending, i.e. by addition of chips of the master batch to the required amount of polyamide chips, or by chip coating, that is forming a paste of the master batch and using this paste to coat polyamide chip.

The nucleating agent can also be incorporated into the polyamide in the correct proportions by a melt-dispersion process, for example, by passing the mixed components through a heated screw extruder optionally combined with a metering pump, for instance a Duplex pump. This method may be used to form a master batch of the nucle- 7 ating agent in the polyamide which may then be further blended with the required amount of additional polyamide by chip blending or chip coating.

The nucleating agent could be incorporated into the polyamide by introducing it into the autoclave during the polymerisation of the polyamide forming salt, or into the polymerisation coil in a continuous polymerisation process.

In processes involving the melt-dispersion of a nucleating agent in a polyamide it is most important that the temperature does not exceed a limit which is dependent upon the optical melting point of the nucleating agent as otherwise the effectiveness of the nucleating agent is lost. We have found that the melt-dispersion temperature should not exceed 1.08, and preferably 1.04, times the optical melting point of the nucleating agent..

Any other convenient method of mixing, such as by the use of a Banbury mill, may be employed. It is most important, however, that the nucleating agent be well dispersed in the polyamide since poor dispersion will result in an inadequately nucleated polymer and the novel filaments of the present invention will not be obtained therefrom.

Nucleated polymer may be extruded into filaments using any conventional spinning method involving filtering the polymer through a conventional filter pack prior to extrusion through spinneret orifices at normal temperatures, egg. of the order of 290 C. as is normally employed in spinning nylon 6.6.

The following examples are illustrative of the ways in which the novel filaments of the present invention may be prepared and of the various compositions of the said filaments. It is to be understood that the examples are not intended to in any way limit the scope of the invention.

EXAMPLE 1 Preparation of a (50:50)6.6:6T copolymer nucleating agent Equivalent molecular proportions of hexamethylene diammonium adipate and hexamethylene diammonium terephthalate and a small amount of Water (used to maintain homogeneity), were mixed together and heated, with continuous agitation, in an autoclave at a temperature of 230 C. and under a pressure of 350 p.s.i. for a period of 3 hours. The low molecular weight polymer was then further polymerised in the solid state by heating at 290 C. in a steam for a period of 5 /2 hours. The copolymer so obtained had an optical melting point of 330 C.

Incorporation of the copolymer nucleating agent into 6.6 nylon The copolymer additive was then incorporated into 6.6 nylon by a solution blending method as follows:

72 gms. of the copolymer additive were dissolved in 648 gms. of 90 percent aqueous phenol percent weight by weight solution) by refluxing and stirring under an atmosphere of nitrogen. Another solution containing 1,368 gms. of polyhexamethylene adipamide having a relative viscosity of 40, was made by dissolving the polyamide in 12,312 gms. of 90 percent aqueous phenol (10 percent weight by weight solution).

The two solutions were mixed, by stirring together, at a temperature of around 40 C., in amounts such that the final ratio of solutes was one part of weight of the copolymer nucleating agent to 19 parts of 6.6 nylon. The homogeneous phenol solution was poured into methanol, and the precipitate filtered off and washed with methanol, and then boiled with water for several days to steam distill off the residual phenol. The precipitate, after drying was in the form of a fairly fine powder (master batch powder).

940 gms. of the master batch powder was homogenised with 2 litres water using an Ultra Turrax high speed mixer to form a paste. 280 gms. pigmentary nylon base 8 (20% pigmentary nylona very finely divided low molecular weight 6.6 nylon+80% water) was also added and mixed in with the master batch powder. This was necessary to ensure satisfactory adherence of the powder to the polymer chip in the final chip coating operation, particularly at the relatively high level required.

The paste prepared as described above was chip coated onto standard production 6.6 nylon chip (relative viscosity 40, 0.3% TiO content) in a Gardner mixer using 8 lb. polyamide chip so that the ratio of master batch powder to the 6.6 nylon chip was 1:4 giving a final level of 1 percent of the copolymer nucleating agent of the coated chip for spinning.

The resultant polymer had a D.T.A. freezing point of 234 C. while a control polymer without nucleant had a D.T.A. freezing point of 223 C.

The polymer was melted in a gravity melter and the melt extruded through a 10 hole spinneret (each hole being 0.013 inch in diameter) into filaments at a rate of approximately 0.054 lb. total polymer per minute at a spinning temperature of 289 C. The filaments were spun into a quenching chamber wherein they were cooled by a transverse stream of air and in which they became solid. The 10 filament yarn so obtained, in which the filaments were each 9 denier, was collected at ambient temperature and relative humidity at a speed of 3930 feet per minute in the form of a yarn package. To provide the comparative information a control yarn, derived from polyhexamethylene adipamide chips having a relative viscosity of 40 and containing 0.3 percent TiO as a delustrant but no copolymer nucleating agent, was spun and collected under identical conditions. The yarn containing the filaments of the present invention had a birefringence value of 0.0101 and the control yarn a value of 0.0185. Both yarns were drawn using a production type drawtwister operating at a drawing speed of 1520 feet per minute. The draw ratios were adjusted for each yarn to give drawn yarn of denier with 0.52 turns per inch twist and with a nominal extension at break of approximately 30 percent.

The yarn containing the filaments of this invention had to be drawn at a draw ratio of 4.40 to produce a yarn with an extension at break of approximately 30 percent while the same extension at break could be obtained in the control yarn by drawing it at a draw ratio of only 3.12. The increase in spinning productivity, arising from the opportunity which was afforded of using larger throughputs of the polymer, was therefore of the order of percent.

Without limiting the invention to any particular theory it is believed that the incorporation of a nucleating agent such as that described in Example 1 in a polyamide infiuences the development of crystallinity in filaments spun from the molten polymer to the end that the filaments solidify nearer the spinneret plate than unnucleated fila ments, with a reduced degree of supercooling at the solidification point. The nucleant also causes the formation of a large number of small optically birefringent regions uniformly distributed throughout the filament to the exclusion of large spherulites, which regions, when viewed in polarised light, do not exhibit any resolvable pattern of preferred orientation such as the well-known extinction patterns normally associated with spherulitic structures and are usually less than 1 micron across.

The influence of the nucleating agent employed in Example 1, i.e. a (:50)6.6:6T copolymer, at varying concentrations, on the D.T.A. freezing point of 6.6 nylon is shown graphically in FIG. 3, in which freezing point is plotted against rate of cooling. The curves in FIG. 3 are identified as follows:

Curve Apolyhexamethylene adipamide with no copolymer nucleating agent Curve B-polyhexamethylene adipamide with 0.05 percent nucleating agent Curve C polyhexamethylene adipamide with 0.1 percent nucleating agent Curve D-polyhexamethylene adipamide with 0.3 percent nucleating agent Curve E-polyhexamethylene adipamide with 1 percent nucleating agent Curve Fpolyhexamethylene adipamide with 3, and

percent nucleating agent The figure shows that the freezing point of the polymer increases with increase in concentration of the nucleating agent up to between 1 and 3% levels, there being little detectable change as the concentration is increased from 3 to 10% (curve F).

FIGS. 4 and 5 show graphically on linear and leg scales respectively, the variation in D.T.A. freezing point of 6.6 nylon containing different amounts of the copolymer nucleating agent. The freezing points being determined at a fixed rate of cooling, i.e. 64 C./min. Little change in freezing point is seen until the concentration of the nucleating agent reaches at least the 0.01% level, the freezing point then increases rapidly up to about the 2% level after which there is little or no increase. A copolymer nucleating agent concentration in the range 0.5 to 1.5% would appear to be a satisfactory working range.

Although the above-mentioned graphs were constructed from results obtained from bulk polymers, the conclusions are equally applicable to filaments spun from the polymer which would normally be cooled at a rate exceeding 64 C./min.

In the further examples described hereinafter the increase in productivity is indicated by the productivity ratio (P.R.) which is defined as:

Draw ratio to yield extension at break for a filament containing nucleating agent -Draw ratio to yield 30% extension at break for a filament without nucleating agent drawing tension nominal stress:

spun denier where spun denier is the denier of the undrawn yarn. Nominal stress is then plotted against draw ratio and the draw ratio at a nominal drawing stress of 0.5 g./d. read off. The determination should be carried out at a temperature of 71.3i2.5 F. and a relative humidity of 67.8% i2.5%, and the drawing tension of the yarn measured between the snubbing pin and draw roll. Comparsion of the draw ratios at a nominal stress of 0.5 g./d. of as-spun filaments containing a nucleating agent with asspun filament without a nucleating agent, clearly shows that higher draw ratios can be achieved with the former.

In order to obtain the filaments of the present invention it is essential that the nucleating agent remain as discrete particles in the polymer during spinning and also during melt dispersion when this method is used to incorporate the nucleating agent in the polymer. It is also important under these circumstances that the holding time of the polymer containing the nucleating agent in the molten state during melt-dispersing and spinning be kept as short as practicable to limit the degree of amide interchange taking place between the polymer and the nucleating agent which would effectively destroy the latter. For the above reasons it is clear that a polymeric nucleating agent should have an optional melting point at least above the melt holding temperature at spinning. Preferably the optical melting point of the nucleating agent is at least 10 C. or even more preferably at least 30 C above the melt holding temperature at spinning.

A polymeric nucleant which has an optical melting point which is considered to be too low to be wholly effective in a particular polyamide system, may have its melting point raised by a heat treatment. Thus it has been estab lished that the optical melting point of a (50:50)6.6:6T copolymer can be raised from 325 C. to 344 C. by heating at 325 C. for 1 hour under steam at atmospheric pressure.

EXAMPLES 2, 3 AND 4 In these examples the base polyarnide was 6.6 nylon (40.R.V. containing 0.3% TiO and the nucleating agent a (50:50)6.6:6T copolymer.

The spinning speed, in these and all subsequent examples, was 3930 f.p.rn. unless stated to be otherwise.

The nucleating agent was prepared by mixing together in the presence of a small amount of water, equivalent molar preparations of hexamethylene diammonium adipate and hexamethylene diammonium terephthal ate. The mixing was carried out in an autoclave with continuous agitation at a temperature of 250 C. and a pressure of 510 p.s.i. for 2 hours. The low molecular weight polymer was further polymerised in the solid state by heating at 290 C. in steam for a period of 5 /2 hours. The optical melting point of the copolymer was 330 C.

Dispersion of the nucleating agent in 6.6 nylon was carried out using the general procedure described in Example 1 with various ratios of base polymer to nucleant employed in the preparation of the master batch. Details of the dispersion of the copolymer nucleating agent in 6.6 nylon base polymer are given in Table 1 below:

TABLE 1 Example 2 3 4 Master batch ratio (nucleantzbase polymer) 1:19 1:0 1:2 Solvent, percent aqueous phenoL 90 90 90 Preeipitant Benzene Methanol Methanol volumeszvolume solvent- 10: 1 10:1 10:1 Chip coating ratio (master base polymer) 1:4 1:9 1:32. 3 Concentration of nucleating agent,

percent 1 1 l D. T. A. freezing point of nucleated polymer, C 233 233 233 tails of spun yarn properties and draw ratios are given in Table 2.

TABLE 2 Example 2 3 4 Spun yarn roperties:

Denier filament 13. 4 13. t] 11. 4 Birefringence 0.0110 0. 0106 0. 0098 Oi 0.21 0.09 0.04 00 0. 57 0. 46 0. 45 01-00- 0. 78 0.55 0.49 D.T.A. freezing point 231 232 232 Draw ratio for 30% extension at break. 4. 36 3. 4. 09 Productivity ratio 1. 39 1. 24 l. 32 Draw ratio at a nominal stress of 0.5 3. 4. 0 2. 50

EXAMPLES 5, '6 AND 7 The present examples illustrate a method of incorporating a nucleating agent in a base polymer by melt-dispersion. The base polymer and a (50:50)6.6:6T polymeric nucleating agent were initially blended together at various nucleant to base polymer ratios by mixing the polymer and nucleant together in the dry state and then melt-dispersing the nucleant by passing it through a screw extruder. The molten polymer containing the disposed nucleating agent was co led, chipped and blended with the base polymer chip to give the correct nucleant concentration. The screw extruder used had a screw diameter of inch and ran at a speed of 25 r.p.rn. The maximum temperature of the barrel of the extruder was 325 C. and the throughput 30 mL/min. giving a polymer transit time in the extruder of approximately 1 minute.

TABLE 4 Example 8 Melt dispersing:

TABLE 3 Ratio nucleating agent to base polymer.

0 Temperature, C Example 6 7 Chip blending:

A Ratio melt mix to base polymer 1:4 Melt dispersing: Concentration of nueleating agent, percent. 1.0 Ratio nueleating agent to base polymer in T A freezing int f 1 m O G master batch 1:00 1:19 1: Spun yarn poperties: Temperature, C 315 325 3'25 Denier/filament 9. 2 0. 0 Chip blending: 10 Birefringenee 0.0112 Ratio melt mix to base polymer 1:4 1: 0 0. 06 51 Concentration of nueleating agent. percent. 1 1 1 0,, 0. 54 0. 71 D.T.A. freezing point of nucleated polymer, 0 -0,, 0.60 0. 2 C 231 229 231 D.T.A. freezing point, C 205 201 bpun yarn properties: Draw ratio for extension at break 3. 88 2. 78 Denier/filament 3- 6 Draw ratio at nominal stress of 0.5... 2.75 1. 10 Birefringence... 0- 0 8 3 Productivity ratio 1. 39 1. 0

O. 0. 53 O. 68 0. 84 0. G1 0. 94 1 D T 4- l g i k 5 33 25 Examples 10, 11 and 12 illustrate the effectiveness in )raw ra 10 or ex ension a )l'fia' Draw ratio at noniinal stress o1'0.5.. 4. 25 3. 84 3. 12 nyl0n of dlflel ent polyamlde Qucleatmg agents Productivity ratio 1. 32 1. 33 1. 0 taming a terephthalamide linkage in the polymer chain.

Example 8 illustrates the eflicacy of a (50:50)6.6:6T copolymer nucleant in increasing the productivity in the manufacture of filaments from 6.8 nylon. Example 9 is a control experiment. The nucleating agent was prepared as in the previous examples and dispersed in the base polymer by the melt-dispersing method. Details of the polymer preparation and spun and drawn yarn properties are given in Table 4.

20 Example 13 is a 6.6 nylon control included for the purpose of comparison. Spinning and drawing of nucleated polymers were carried out under the conditions previously described. Details are given in Table 5.

TABLE 5 Example 10 11 12 13 Nueleating agent (50:50)0.0:0.T. (3.1 nylon 10.T nylon Method of dispersing nue Melt-dis- Solution Meltdisagent. persing. blending. persing. Temperature of melt-dispersing, 325 340 Ratio nueleating agent to base 1:0 1:10 1:10

polymer in master batch. Chip blending/chip coating ratio, 1:0 1:4 1:4

master batch to base polymer. Concentration of nueleating agent, percent.

1 The solvent was aqueous phenol and precipitant methanol.

The following examples, l4-l9, compare the effectiveness of various concentrations, from 0.01% to 5.0% by weight, of the preferred nucleating agent (50:50)6.6:6.T

nylon, in 6.6 nylon containing 0.3% TiO Details are 0:)

shown in Table 6.

TABLE 6 Example 14 15 16 17 18 19 Method of dispersing nueleating agent- Temperature of melt dispersing, C 325 325 Ratio nucleating agent to base polymer in master batch. 1:10 1:10 1:10 1:10 1 2 1:10 Chip blending/chip coating: ratio master batch to base polymer 1:400 1:40 1:0 1 4 1:32. 2 Concentration of nueleating agent, percent. 0. 01 0. 1 0. 5 1 0 2. 0 5 0 D.T.A. freezing point, C 232 233 Spun yarn roperties:

Denier filament- 10. 0 12. 4 13.1 Birefringence- 0. 0103 0 0003 0.0125 Oi 0. 37 0.07 0.15 0D.-. O. 51 0. 38 0. 53 Oi-O..- 0.14 0.45 0. 68 D.T.A. freezing poin 220 231 220 Draw ratio for 30% extension at break. 3. 52 4.05 4. 20 Draw ratio at nominal stress 01 0.5 1. S8 4. l5 4. 0 Productivity ratio 1. 05 1. 20 1. 37

1 Sol. blending. 2 Melt-dispersing:

The above examples indicate that, in the particular system employed and under the conditions of dispersion used, 0.01% of the nucleating agent is insufficient to yield filaments according to the present invention. Thus O O is less than 0.2, there is substantially no increase in productivity, and the draw ratio at a nominal stress of 0.5 g./d. and draw ratio for 30% extension at break is lower than for the remaining examples which illustrate the invention. There are however indications that nucleation had occurred since the spun yarn has an increased D.T.A. freezing point compared with the control yarn of Example 13. The results also indicate that there is no advantage in using a concentration of nucleating agent exceeding 0.1%, although in practice a concentration of between about 0.5% and 1.5% would be preferred for purely technical reasons associated with obtaining an adequate degree of dispersion of the nucleant.

Examples 20, 21 and 22 illustrate the use of different proportions of 6.6 and GT nylons in the preferred copolymer nucleant at the 1% level of nucleant in 6.6 nylon. In Example 20 the nucleating agent was prepared by mixing together aqueous solutions of hexamethylene diamrnonium adipate and hexamethylene diammonium terephthalate, in the correct proportions by weight, and polymerizing the mixture as a continuous process in a coil such as that described in British patent specification No. 924,630. In Examples 21 and 22 the nucleating agents were prepared by the normal procedure adopted in the batch preparation of 6.6 nylon polymer. The nucleating agents were melt-dispersed with the 6.6 nylon to give a master batch and the master batch chip blended with 6.6 nylon chips to give a final concentration of 1% by weight of the nucleating agent in 6.6 nylon. Details are shown in Table 7.

TABLE 7 Example 20 21 22 Ratio nucleating agent to base polymer in mastel-batch 1:99 1:19 1:9 Temperature of melt-dispersing, C 335 315 295 Ratio master batch to base polym in chip blend 1 1:9 Ratio 6.6:6.T nylon in nucleant 45:55 55:45 60:40 Spun yarn roperties:

Denier filament 12. 13. 3 9. 0

Birefringence.

Or-Oo 0. 80 0. 26 0. 26

D.T.A. freezing point, C 230 231 232 Draw ratio for 30% extension at brea 8. 99 3. 82 3. 43 Draw ratio at nominal stress of 0.5.. 3. 52 2. 78 Productivity ratio 1. 28 1. 23 1. 11

EXAMPLE 23 Table 8 Spinning speed, f.p.m. 2930 Spun denier, d.p.f 66 D.T.A. freezing point C. 233 O 0.33 0., 0.51 l- 0.84 Draw ratio for 30% extension at break 4.20

Since a 66 d.p.f. monofil can normally only be spun at speeds up to 1548 f.p.m. it is clear that the presence of the nucleating agent resulted in a considerable increase in productivity at spinning.

The yarn could be drawn at speeds up to 4,500 f.p.m. using a snubbing pin heated to 110125 C. at draw ratios of 4.0 to 4.2 to yield a drawn yarn having a tenacity of 4.34 g./d., extension at break of 29.3% and an initial modulus of 26.5 g./d./ extension.

EXAMPLE 24 This example illustrates the eifect of melt-dispersing a (50:50) 6.6:6.T copolymer nucleating agent having an optical melting point of 330 C., in 6.6 nylon at high temperature. Details are given in Table 9.

Table 9 Temperature of melt-dispersion, C 361 Ratio nucleating agent to base polymer 1:99 Concentration of nucleating agent, percent 1 Spun yarn properties:

Denier/filament 48 Birefringence 0.0128 0 --0.32 0 0.4S (1 -0, 0.13 D.T.A. freezing point, C. 220 Draw ratio for 30% extension at break 3.12 Draw ratio at normal stress of 0.5 2.78 Productivity ratio 1.00

The temperature employed in melt-dispersing the nucleating agent in the polymer was greater than that preferred, i.e. 1.08 times the optical melting point of the nucleating agent, and in consequence there was no increase in productivity and a yarn according to the present invention was not obtained.

What we claim is:

1. A process to increase the process productivity in the manufacture of a yarn comprising one or more melt spun undrawn polyamide filaments comprising incorporating a finely divided polyamide nucleating agent, having a diameter in the spun filament of less than about 0.4 micron and an optical melting point higher than the melt holding temperature of the polyamide at spinning, into a fiber-formable polyamide in a quantity suflicient so that said undrawn filaments have molecular orientation exhibiting X-ray deflection patterns in which (0 0 is greater than 0.2, forcing the said fiber-formable polyamide containing the nucleating agent in a molten state through a filtering medium, extruding the filtered polyamide through orifices contained in a spinneret plate to produce filaments, solidifying the filaments and winding up the said filaments.

2. A process according to claim 1 wherein the nucleating agent limits spherulite growth to spherulite particle sizes below about 1.5 microns in diameter.

3. A process according to claim 2 wherein at least 0.05% by weight of the nucleating agent is incorporated in the fiber formable polyamide.

4. A process according to claim 3 wherein 0.5% to 1.5% by weight of the nucleating agent is incorporated in the fiber formable polyamide.

5. A process according to claim 2 wherein the nucleating agent is incorporated into the polyamide by initially forming a solution of the polyamide and an excess of the nucleating agent in a common solvent, coprecipitating the polyamide and the nucleating agent to form a master batch of the nucleating agent in the polyamide, forming the master batch into a paste, coating the said master batch paste onto more of the polyamide in chip form to give the required concentration of nucleating agent in the said polyamide and melting the polyamide and master batch paste together at spinning.

6. A process according to claim 2 wherein the nucleating agent is incorporated in the polyamide by melt dispersing the said nucleating agent in the said polyamide prior to the melt extrusion of the polyamide into filaments.

7. A process according to claim 6 wherein the melt dispersion is solidified, formed into chips and subsequently melt-extruded into filaments.

8. A process according to claim 6 wherein the meltdispersing of the nucleating agent in the polyamide is carried out in a screw extruder.

9. A process according to claim 6 wherein the temperature of melt-dispersing is less than 1.08 times the optical melting point of the nucleating agent.

10. A process according to claim 9 wherein the temperature of melt-dispersing is less than 1.04 times the optical melting point of the nucleating agent.

11. A process according to claim 2 wherein the nucleating agent is incorporated into the polyamide by meltdispersing an excess of the said nucleating agent in the said polyamide to form a master batch, forming the master batch into a paste, coating the said master batch paste onto more of the polyamide in chip form to give the required concentration of nucleating agent in the said polyamide and melting the polyamide and master batch paste together at spinning.

12. A process according to claim 11 wherein the meltdispersing of the nucleating agent in the polyamide is carried out in a screw extruder.

13. A process according to claim 11 wherein the temperature of melt-dispersing is less than 1.08 times the optical melting point of the nucleating agent.

14. A process according to claim 13 wherein the temperature of melt-dispersing is less than 1.04 times the optical melting point of the nucleating agent.

15. The process of claim 1 wherein the differential thermal analysis freezing point of the nucleated polymer is at least 5 C. higher than the freezing point of the non-nucleated polymer.

16. The process of claim 1 wherein said fiber-formable polyamide is selected from the class consisting of polyhexamethylene adipamide and polyhexamethylene suberamide.

17. The process of claim 16 wherein the polyamide is polyhexamethylene adipamide.

18. The process of claim 1 wherein the polyamide nucleating agent contains a repeating aryl group in the polymer chain.

19. The process of claim 18 wherein the polyamide nucleating agent is a poly(methylene) terephthalamide polymer wherein x is an integer between 2 and 12.

20. The process of claim 18 wherein the terephthalamide polymer nucleating agent is a copolymer with an aliphatic polyamide monomer.

21. The process of claim 20 wherein the copolymer is a poly(hexamethylene adipamide/hexamethylene terephthalamide) copolymer containing at least 30% by weight hexamethylene terephthalamide.

References Cited UNITED STATES PATENTS 2,205,722 6/1940 Graves 26037 2,266,368 12/1941 Hull et a1. 18-85F 3,099,067 7/1963 Merriam et al. 28-82 3,303,169 2/1967 Pitzl 264--210F 3,329,557 7/1967 Magat et al. 161-172 3,367,926 2/1968 Voeks 260-935 3,368,992 2/1968 Albermatt 260-292 3,382,305 5/1968 Breen 264-171 3,393,252 7/1968 Zimmerman 260857 3,432,575 3/1969 Zimmerman 260-857 3,405,211 10/1968 Cancio 264210F 3,434,278 3/1969 Martin et al. 57-157 JAY H. WOO, Primary Examiner US. Cl. X.R. 

